Photosynthetic responses of cassava cultivars (Manihot esculenta Crantz) from different habitats to temperature

Maximum photosynthetic CO₂ exchange rates (P_n) of single attached leaves were determined for several cassava cultivars selected from different habitats and grown in pots outdoors at CIAT, Colombia, S.A. P_n rates were in a narrow range of 22 to 26 mol CO₂ m^–2s^–1 for all cultivars tested when measured at high photon flux density, normal air, optimum temperature and with low leaf-air vapor pressure differences. For all tested cultivars (9 cvs.), there was a broad optimum temperature for P_n between 25 to 35°C. At temperatures below and above this range P_n declined in all cultivars with P_n rates reaching 80% of maximum at 20 and 40°C. P_n temperature coefficient (Q₁₀) from 15–25°C was 1.6±0.2 across cultivars. No consistent relation existed between P_n, optimum temperature, and the original habitat.     

Life tables and predation activity of Orius laevigatus and O. albidipennis at three constant temperatures

Effects of three constant temperatures (15, 25, and 35 -C) on development and reproduction of Orius laevigatus (Fieber) and O. albidipennis (Reuter) (Heteroptera: Anthocoridae) and on their predation activity against the western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) were investigated in the laboratory. Small rooted plants of Spanish pepper (Capsicum annuum L. cv. Creta, long red) served as oviposition substrate and moisture source. Survival of eggs and nymphs of both species was high at 25 and 35 °C. At 15 °C, none of the eggs of O. albidipennis hatched and the number of nymphs completing the immature stage was extremely low. Developmental time of nymphs was not significantly different between species at 15 °C, but at 25 and 35 °C nymphs of O. laevigatus took significantly longer to develop than those of O. albidipennis. Females of O. albidipennis lived longer than those of O. laevigatus at 15 and 35 °C, but no differences were observed at 25 °C. Fecundity of O. albidipennis was greatly reduced at 15 °C, whereas a temperature of 35 °C was close to the upper reproduction threshold of O. laevigatus. Fecundity was highest at 25 °C for both species. At 15 °C, the intrinsic rate of increase (r_m) reached a minimum for both species. For O. albidipennis, the r_m-value increased with temperature (0.121 at 25 °C and 0.202 at 35 °C), whereas for O. laevigatus it peaked at 25 °C (0.105) but decreased at 35 °C (0.051). At 15 and 25 °C, adults of O. laevigatus consumed more F. occidentalis adults during their total lifespan than those of O. albidipennis, but the latter showed a better predation activity at 35 °C; in all treatments, however, adults of O. laevigatus consumed more prey per day than did those of O. albidipennis. The performance of both anthocorids at the different temperatures is discussed in relation to their practical use in integrated pest control programmes.     

Aspects of the respiratory biology of two New Zealand intertidal fishes, Acanthoclinus fuscus and Forsterygion sp

Synopsis Aerial and aquatic VO₂ measurements of Acanthoclinus fuscus and Forsterygion sp. showed that A. fuscus weighing up to 25 g obtained oxygen from air and water at similar rates, whereas the ratio of aerial to aquatic VO₂ for F. sp. was mass dependent. The Q₁₀ for aquatic respiration of A. fuscus and F. sp. was found to be 2.3 and 2.5, respectively. Aerial VO₂ measurements showed that A. fuscus could continue to increase its aerial VO₂ up to at least 25° C. In contrast the aerial VO₂ of F. sp. increased only between 5° C and 15° C and decreased between 20 and 25° C. The P_crits of both A. fuscus and F. sp. were found to be about 35 torr. Emergence in response to hypoxia occurred between 0 and 16 torr which suggested active emergence was an oxykinetic response and not a behaviour.to whom all correspondence should be addressed     

Air Breathing and Gill Ventilation Frequencies in Juvenile Tarpon, Megalops atlanticus: Responses to Changes in Dissolved Oxygen, Temperature, Hydrogen Sulfide, and PH

This study quantified the air-breathing frequency (ABf in breaths h^–1) and gill ventilation frequency (Vf in ventilations min^–1) of tarpon Megalops atlanticusas a function of PO₂, temperature, pH, and sulphide concentration. Ten tarpon held at normoxia at 22–33°C without access to atmospheric oxygen survived for eight days, and seven survived for 14 days (at which point the experiment was terminated) suggesting that the species is a facultative, rather than an obligate, air breather. At temperatures of 29°C and below ABf was highest and Vf was lowest at low oxygen partial pressures. Tarpon appear to switch from aquatic respiration to air breathing at PO₂levels of roughly 40 torr. The gills were the primary organ for oxygen uptake in normoxia, and the air-breathing organ the primary mechanism for oxygen uptake in hypoxia. At 33°C, both ABf and Vf were elevated but highly variable, regardless of PO₂. There were no mortalities in tarpon exposed to total H₂S concentrations of 0–232µM (0–150.9µM H₂S); however, high sulfide concentrations resulted in very high ABf and Vf near zero. Vf was reduced when pH was acidic. We conclude that air breathing provides an effective means of coping with the environmental conditions that characterize the eutrophic ponds and sloughs that juvenile tarpon typically inhabit.     

Effect of temperature and oxygen on cell growth and recombinant protein production in insect cell cultures

The effect of temperature and O₂ saturation on the production of recombinant proteins -galactosidase and human glucocerebrosidase by Spodoptera frugiperda cells (Sf9) infected with recombinant Autographa californica nuclear polyhedrosis virus was investigated. The rates of cell growth, glucose consumption, O₂ consumption and product expression were measured at temperatures between 22° C and 35° C. The results indicated that possible O₂ limitation may be alleviated without compromising the maximum cell yield by lowering the incubation temperature from 27° C to 25° C. The expression level of the recombinant proteins at 27° C was similar to that obtained at 22° C and 25° C; lower protein yields were obtained at 30° C. An increase in temperature from 22° C to 27° C led to earlier production of the proteins and to an increase in the proportion of the product released outside the cells. Correspondence to: J. Shiloach     

Thermoregulation,gas exchange,and ventilation in Adelie penguins (Pygoscelis adeliae)

Summary Adelie penguins (Pygoscelis adeliae) experience a wide range of ambient temperatures (T _a) in their natural habitat. We examined body temperature (T _b), oxygen consumption ( ), carbon dioxide production ( ), evaporative water loss ( ), and ventilation atT _a from –20 to 30 °C. Body temperature did not change significantly between –20 and 20°C (meanT _b=39.3°C).T _b increased slightly to 40.1 °C atT _a=30°C. Both and were constant and minimal atT _a between –10 and 20°C, with only minor increases at –20 and 30°C. The minimal of adult penguins (mean mass 4.007 kg) was 0.0112 ml/[g·min], equivalent to a metabolic heat production (MHP) of 14.9 Watt. The respiratory exchange ratio was approximately 0.7 at allT _a. Values of were low at lowT _a, but increased to 0.21 g/min at 30°C, equivalent to 0.3% of body mass/h. Dry conductance increased 3.5-fold between –20 and 30°C. Evaporative heat loss (EHL) comprised about 5% of MHP at lowT _a, rising to 47% of MHP atT _a=30°C. The means of ventilation parameters (tidal volume [VT], respiration frequency [f], minute volume [I], and oxygen extraction [ ]) were fairly stable between –20 and 10°C (VT did not change significantly over the entireT _a range). However, there was considerable inter- and intra-individual variation in ventilation patterns. AtT _a=20–30°C,f increased 7-fold over the minimal value of 7.6 breaths/min, and I showed a similar change. fell from 28–35% at lowT _a to 6% atT _a=30°C.Abbreviations C thermal conductance - EHL evaporative heat loss - oxygen extraction - f respiratory frequency - MHP metabolic heat production - evaporative water loss - LCT lower critical temperature - RE respiratory exchange ratio - T _a ambient temperature - T _b body temperature - rate of oxygen consumption - rate of carbon dioxide production - I inspiratory minute volume - VT tidal volume     

Incubation water loss,shell conductance,and pore dimensions in Adelie Penguin eggs

Summary In order to understand water loss regulation of bird eggs in very dry climates eggs of the Adelie Penguin were studied at Cape Bird, Ross Island, Antarctica. During incubation 125 g Adelie Penguin eggs lose about 447 mg of water per day, resulting in an overall estimated loss, during 35 days of incubation, of 13% of their initial mass. The eggshell conductance of 13.1 mg H₂O·day^-1·torr^-1 occurs from 9100 pores with an effective radius and pore length of 11 m and 600 m, respectively. In this study the water vapor pressure of the egg was 44 torr, estimated from the egg temperature of 35.9°C. Ambient temperature was-4°C, with an absolute humidity of less than 3 torr, resulting in an overall vapor pressure difference between the egg and the environment of 41 torr. This difference was divided between the egg and nest conductance in a ratio of ca. 1:5.     

Effects of temperature on the rates of oxygen consumption during morphogenesis and diapause in the egg stage of Letopterna dolobrata (Heteroptera,Miridae)

Summary Oxygen consumption at 25°C was measured continously throughout the egg stage of Leptopterna dolobrata (more than 9 months).The rate of O₂-uptake (l O₂/100 eggs · 1 h) is low in freshly laid eggs. Maintaining the eggs at a constant temperature of 16°C, respiration rises abruptly from the first day after oviposition and continues rising steadily for 3 days, reaching an average value of 1.4 l. Oxygen consumption persists at or near this high level during the developmental phase of prediapause, which lasts about 15 days. After some days of oscillating high and low values, respiration decreases, and from the 24th day a low level (0.3–0.4 l) is reached. If the eggs are incubated at 16°C continuously, this low diapause-level is maintained until the end of the experiments (42 weeks) and diapause is terminated in a few eggs only.A significant increase in the success of hatching is obtained by exposing the eggs to a sufficient period of chilling.24 groups of diapausing eggs were chilled at 5°C for certain periods (10, 18, 22, 26, 31, and 34 weeks) and afterwards transferred to 16°C and re-incubated. The changes of their O₂-uptake at 25°C were traced throughout their chilling and successive re-incubating periods.Oxygen consumption is greatly accelerated during the cold treatment of the eggs. The low values of the diapause-level are raised progressively during the first 6 weeks of chilling. After this primary rapid increase, respiration remains at a level 5-times as high as the diapause values over a period up to the 25th week at 5°C. This is almost exactly the duration of mesodiapause (6 months).The rates of O₂-uptake during the subsequent re-incubation at 16°C depend on the extent of chilling. The ability of diapause-breaking is correlated to the rates of O₂-uptake, measured after setting of re-incubation. If respiration never decreases by the onset of re-incubation, diapause is terminated in most of the eggs, and the rates of O₂-uptake increase as re-incubation goes on towards the emergence of the larvae (postdiapause period).A preliminary interpretation of the cold-stimulated O₂-uptake in diapausing Leptopterna-eggs is given.Dedicated to Prof. Dr. H. Precht (Kiel) on the occasion of his 65th birthday     

Chlorophyll a Fluorescence Analysis in Response to Excitation Irradiance in Bean Plants (Phaseolus vulgaris L. and Vigna unguiculata L. Walp) Submitted to High Temperature Stress

Bean plants Phaseolus vulgaris L. (cv. Carioca and Negro Huasteco) and Vigna unguiculata L. Walp (cv. Epace-10) were grown in a growth chamber with a photosynthetic photon flux density of 200 mol m^–2 s^–1 at leaf level and air temperature of 25+1 °C. Fully expanded, first pair leaves of 12-d-old plants were submitted for 90 min to high temperature (25, 30, 35, 40, 45, and 48 °C). Chlorophyll a fluorescence parameters (ETR, q_P, q_N, and F₀) were investigated using a modulated fluorimeter at 25 °C during recovery considered here as 48 h after stress induction period. An accentuated decrease in q_P and an increase in q_N at 48 °C in Carioca and Negro Huasteco was not observed in Epace-10. In response to excitation irradiance a great potential for ETR was found in Negro Huasteco at 25 °C, also demonstrated by net photosynthetic rate. At 48 °C ETR was high for Epace-10 while it was equal to zero for Carioca and Negro Huasteco. Tolerance to high temperature observed in Epace-10 provided important information about the adaptative characteristics of Vigna cultivars to warm climates.     

Responses of florence fennel (Foeniculum vulgare azoricum) seeds to light,temperature and gibberellin A4/7

The percentage and the rate of germination of seeds of three varieties of Florence fennel was higher in the dark than in the light, the high temperature cut-off points being between 27.2 and 29.4°C. The optimum temperature for germination was between 20 and 25°C. Seeds of all three varieties responded to incubation in solutions containing gibberellin A_4/7 mixture (GA_4/7; Regulex), giving higher germination in the light at temperatures from 20 to 30°C. Seeds steeped for 4 h at 25°C or for 24 h at 5°C in GA_4/7 solutions gave a higher percentage and increased rate of emergence as compared with untreated dry seeds, when sown in compost at 25°C; steeping in water alone was also beneficial. In general, drying the treated seeds before sowing reduced the rate but sometimes increased the percentage of germination as compared with seeds sown when still moist. Seeds harvested from secondary umbels of var. Zefa fino germinated better both in the light and dark than those taken from primary umbels.Abbreviations GA_4/7 a commercial mixture of the gibberellins A₄ and A₇ (trade name Regulex)     

Kinetics of bacteriophage lambda repressor synthesis directed by the PRE promoter: influence of temperature, multiplicity of infection, and mutation of PRM or the cro gene

Summary Expression of the P _RE (establishment) pathway for repressor synthesis is regulated both by phage-specific genetic elements and by physiological conditions. Here we describe the effects of temperature, multiplicity of infection, mutations in the cro gene, and a mutation in P _RM on P _RE-directed repressor synthesis. As Reichardt (1975a) has shown, repressor synthesis begins 5–15 min after infection by wildtype phage, and is shut off at 20–30 min after infection, depending on the temperature. At 43°, synthesis starts sooner, shuts off earlier, and leads to lower repressor levels than are attained at lower temperatures. Experiments with the temperature sensitive mutant crots20 demonstrate that, as had been shown previously in experiments at 30° and 37° C, cro protein is responsible for the shut-off of repressor synthesis at 43°. In addition to the effects of temperature, the kinetics of repressor synthesis are strongly affected by multiplicity of infection (moi). At mois greater than 10, repressor synthesis after infection by wildtype at 30° is dramatically inhibited. Unexpectedly, the P _RM mutation prm116, under certain conditions, can alleviate both cro-mediated shutoff and the inhibition of P _RE-directed repressor synthesis at high moi. These effects of prm116 are observed only at low temperature (30°–32° C) and at mois of about 6–10 or greater; they also appear to be cis-specific. Possible mechanisms for the effects of the prm116 mutation are discussed. Finally, these studies demonstrate that crots20, which was isolated as a temperature-sensitive lethal mutation in the cro gene (Herskowitz, unpublished), is temperature-sensitive with respect to the ability to shutoff P _RE-directed repressor synthesis; however, even at low temperature (30° C), the crots20 gene product is only partially active.     

Effects of high ambient temperatures on the metabolism of West African dwarf goats. II

32 West African dwarf goats were exposed in respiration chambers to temperature treatments of 20, 25, 30, 35, 35, 35, 30, 25, 20°C. Each treatment lasted three days. 16 goats were kept in individual pens (I); the others in two group pens of eight animals each (G). During each treatment, heat production and activity were recorded continuously over 48 hours. In addition, feed and water intake, rectal temperature, skin temperature and respiratory rate were measured during each treatment.Compared to 20°C, at 35°C rectal temperature increased from 39.0°C to 39.9°C, respiratory rate from 30 to 260 times. min^–1 and skin temperature from 37.1°C to 39.5°C. Hay intake decreased by 40%; concentrates (30 g. kg^–0.75. d^–1) were always completely consumed. Heat production was higher for the G animals at 20°C and higher for the I animals at 35°C. These differences in heat production between the two groups were reflected in differences in rectal and skin temperature and in respiratory rate but only very slightly in differences in hay intake.Tissue insulation was 0.014 K. m². W^–1 at 30°C and 35°C and 0.022 K. m². W^–1 at 20°C.It is concluded that the reactions of these dwarf goats to high ambient temperatures are not different in principle from those of other domestic ruminants and that they do not exhibit a specific suitability or unsuitability for ambient temperatures as prevailing in West Africa.     

Development, survival and reproduction of Euseius finlandicus (Acari: Phytoseiidae) at different constant temperatures

Development, survival and reproduction of Euseius finlandicus Oudemans were studied at seven constant temperatures (15, 20, 25, 27, 30, 32 and 34°C) in the laboratory. Within the temperature range tested, developmental period from egg to adult varied from 148 to 360.5h and 133.7 to 336.5h for females and males, respectively. The lower thermal threshold for immature development for females and males was 8.9 and 6.4°C, respectively. Survival during immature development exceeded 90% at all the temperatures from 15 to 32°C, but at 34°C an abrupt decline was recorded. Female longevity decreased gradually from 82.7d at 15°C to 12.2 d at 34°C. The mean generation time ranged from 44.3d at 15°C to 15.9d at 32°C. The highest r _m value (0.2817) was obtained at 30°C and the lowest at 15°C (0.0976). Temperatures above 30°C had an adverse effect on population increase.     

Effect of constant temperatures on germination, radial growth and virulence of Metarhizium anisopliae to three species of African tephritid fruit flies

The effect of temperatureon conidial germination, mycelial growth, andsusceptibility of adults of three tephritidfruit flies, Ceratitis capitata(Wiedemann), C. fasciventris (Bezzi) andC. cosyra (Walker) to six isolatesof Metarhizium anisopliae were studied inthe laboratory. There were significantdifferences among the isolates in the effect oftemperature on both germination and growth.Over 80% of conidia germinated at 20, 25 and30°C, while between 26 and 67% conidiagerminated at 35°C and less than 10% at15°C within 24 hours. Radial growth was slowat 15°C and 35°C with all of theisolates. The optimum temperature forgermination and mycelial growth was 25°C. Mortality caused by the six fungal isolatesagainst the three fruit fly species varied withtemperature, isolate, and fruit fly species.Fungal isolates were more effective at 25, 30and 35°C than at 20°C. The LT₉₀values decreased with increasing temperature upto the optimum temperature of 30°C. Therewere significant differences in susceptibilitybetween fly species to fungal infection at allthe temperatures tested.     

Effects of day-to-day changes in root temperature on leaf conductance to water vapour and CO2 assimilation rates of Vigna unguiculata L. Walp.

Summary Leaf gas exchange of Vigna unguiculata was influenced by short-term (day-to-day) changes in soil temperature and the response depended upon the aerial environment. When aerial conditions were constant at 30° C leaf temperature, high air humidity and moderate quantum flux, CO₂ assimilation rate and leaf conductance increased with increases in soil temperature from 20 to 35° C, and this response was reversible. Decreases in CO₂ assimilation rate and leaf conductance were observed at root temperatures above 30° C when root temperatures were increased from 20° C to 40° C and when air humidity was decreased in steps during the day. In contrast, varying soil temperatures between 20 to 35° C had no influence on gas exchange when shoots were subjected to a wide range of temperatures during each day.The gain ratio A/E remained constant at different air humidities when root temperature was less than or equal to 30° C indicating optimal gas exchange regulation, but changed with humidity at higher root temperatures. Leaf conductance responded independently from leaf water potential which remained relatively constant during individual experiments.The results indicate that plant responses to high root temperatures may have relevance to plant performance in semi-arid environments. They also illustrate the importance of controlling soil temperatures when studying the responses of potted plants in controlled aerial environments.Dedicated to K.F. Springer     

Growth and reproduction of the mosquitofish,Gambusia affinis,in relation to temperature and ration level: consequences for life history

The allocation of energy to growth and reproduction, in relation to temperature and food availability, was investigated in laboratory experiments with the mosquitofish,Gambusia affinis. At constant temperature of 20, 25 and 30°C and ad libitum feeding, specific growth rates increased with increasing temperature at 1.7, 3.1 and 3.4% dry mass day⁻¹, respectively. Growth rates in a cycling temperature regime (20–30°C, ) were faster than in a 25°C constant temperature. As temperature increased from 20 to 30°C, mean age at first reproduction decreased from 191 to 56 days and brood size and mass of offspring increased significantly. Interbrood interval was also temperature dependent; estimates at 25 and 30°C for females >1000 mg were 22.6 and 18.6 days, respectively. Interbrood interval could not be calculated at 20°C. Although fitness was highest at 30°C, females at 25°C invested a greater proportion of surplus energy (growth and reproduction) to reproduction (38%) than at 20 (17%) or 30°C (36%) during the 32-week study. Fish at cooler temperatures began reproduction at a smaller size. Where rations were controlled at low, medium, and ad libitum levels, somatic and gonadal growth increased with increasing temperatures and food availability. The proportion of energy invested in reproduction was highest at 25°C for each comparable ration level. Calculated energy budgets indicated that over the 10-week study, 17–22% of the food energy was invested in growth, 0–7% in reproduction, and 75–83% in respiration and excretory losses, depending on feeding and temperature conditions.     

Photosynthetic performance of transplanted ecotypes ofEcklonia cava(Laminariales, Phaeophyta)

Young sporophytes of short-stipe ecotype ofEcklonia cavafrom a warmer locality (Tei, Kochi Pref., southern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the transplanted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were assessed per unit area, per unit chlorophyllacontent and per unit dry weight. In photosynthesis-light curves at 10–29 °C, light saturation occurred at 200–400 mol photon m^–2s^–1in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate (P _max) at 10–29 °C and the light-saturation index (I _k) at 25–29 °C in sporophytes from both localities were generally higher in winter than in summer.P _maxat 25–29 °C (per unit area and chlorophylla) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 °C in winter and 27 °C in summer at high light intensities of 100–400 mol photon m^–2s^–1. However, at lower light intensities of 12.5–50 mol photon m^–2s^–1, it was 20 °C in winter and 25–27 °C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 °C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation.     

Effect of temperature on hatching and nest site selection in the Green lynx spider, Peucetia viridans (Araneae:Oxyopidae)

1.

Thirty-seven Peucetia viridans egg sacs were incubated at 15, 17.5, 20, 25, 30, 32.5 or 35 °C. Hatching time was inversely proportional to temperature, and no hatching occurred at the extremes (15, 17.5 and 35 °C).     

Influence of temperature on bionomics of cotton aphid, Aphis gossypii, on cotton

Life table parameters of Aphis gossypii Glover (Homoptera: Aphididae) on Gossypium hirsutum L. were determined at six temperatures (10, 15, 20, 25, 30, and 35 ± 0.5°C) in the laboratory. Relationships of life table parameters with temperature were described with mathematical equations. Development was fastest at 30°C, with a pre-larviposition period of 4.6 d. Survival to adult was greatest at 25°C (81%). Fecundity was highest at 25°C, with a total fecundity of 28.3 nymphs per female and a mean reproductive rate of 3.1 nymphs per female per day. Threshold temperatures for development in the first through fourth instar and the adult were 8.2, 8.0, 7.2, 6.2 and 7.9°C, respectively. The durations of these stages, expressed as temperature sums above these thresholds, were 24.2, 23.7, 23.0, 25.5 and 168.8 degree-days (D°), respectively. A. gossypii achieved its maximum net reproductive number (24.4 nymphs per female) and greatest intrinsic rate of increase (0.386 d–1) at 25°C. The high relative rate of population increase at 25°C results in a daily population increase of 47% and a doubling time of only 1.8 d, illustrating the tremendous growth capacity of A. gossypii populations under favourable conditions. Compared to literature sources, our source of A. gossypii, fed on cotton, showed a comparatively great heat tolerance.     

Temperature-Dependent Gas Exchange and Stomatal/Non-Stomatal Limitation to CO2 Assimilation of Quercus Liaotungensis under Midday High Irradiance

The effects of varying leaf temperature (T ₁) on some ecophysiological characteristics of photosynthesis for Quercus liaotungensis Koiz. under ambient radiation stress around midday on clear summer days were investigated using an IRGA equipped with a temperature-controlled cuvette. Net photosynthetic rate (P _N) decreased as T ₁ increased from 30 to 35 °C as a result of stomatal closure, whereas non-stomatal limitation led to decreased P _N in the T ₁ range of 35–45 °C. Decreased transpiration rate (E) and stomatal conductance (g _s) at leaf temperatures above 30 °C were interpreted as a combined feedward effect as a result of enhanced leaf-air vapour pressure deficit (VPD) and stomatal closure. Changes in E from T ₁ 30 to 20 °C depended on VPD when g _s was maintained constant. Water use efficiency (WUE) varied inversely with T ₁ by following a hyperbola. A decrease in intercellular CO₂ concentration (C _i) occurred as a result of stomatal closure and a relatively high carboxylation capacity, whereas inactivation of mesophyll carboxylation in combination with photorespiration might be associated with the observed increase in C _i in the T ₁ range of 40 to 45 °C.